Pressure axial-piston machine with rotating drum under axial force generated by fluid



Feb. 17, 1970 o. KnA-rtsnaznfiu v 339 5 PRESSURE AXIAL-PISTON MACHINE: WITH ROTATING DRUM UNDER AXIAL FORCE GENERATED BY FLUID Filed July 12, 1968 ZSheets-Sheet 1" FIG.)

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BY 4 magma ATTORNEY D. IKIZATZEIIBEEG.

' Feb. 17, 1970 o. KRM'zsNaaRG 1 3 5, I I PRESSURE AXIAL-PISTON MACHINE WITH ROTATING DRUM Filed July 12. 1968 H5 H4 I 15' 0. kRATZEHB EEG.

m w e m S m an 5 Re ATTORNEY United States Patent 3,495,542 PRESSURE AXIAL-PISTON MACHINE WITH ROTATING DRUM UNDER AXIAL FORCE GENERATED BY FLUID Dietrich Kratzenberg, Haibach, Franz Forster, Karlstadt, and Gerd Ahrens, Hosbach, Germany, assignors to Linde Aktiengesellschaft, Wiesbaden, Germany, a corporation of Germany Continuation-impart of application Ser. No. 597,944, Nov. 30, 1966. This application July 12, 1968, Ser. No. 744,489 Claims priority, application Rumania, July 13, 1967,

The portion of the terni of the patent subsequent to Nov. 12, 1985, has been disclaimed Int. Cl. F04b 1/02 US. Cl. 103-162 9 Claims ABSTRACT OF THE DISCLOSURFL An axial-piston machine (e.g. axial-piston hydraulic pump or motor) having a cylindrical drum in which the working pistons are axially reciprocable and is journaled on an axially shiftable but nonrotatable central shaft retaining the drum axially via an antifriction means (e.g. roller or hydrostatic bearings) under hydraulic pressure applied at a single annular shoulder of the piston along two coaxial zones with respective chambers connected to different pressure regions of the machine.

This application is a continuation-in-part of our application Ser. No. 597,944, filed Nov. 30, 1966, now US. Patent No. 3,410,220.

In the commonly assigned US. Patents No. 3,261,421

and No. 3,279,173, there is described a class of axialpiston machines generally employed in hydrostatic hydraulic transmissions and mechanisms. Such machines comprise a rotatable cylinder drum journaled within a housing for rotation with or relatively to, a fluid-control, fluid-distribution or valve plate or apertured surface pro vided in or formed by the housing of the machine.

The angularly spaced annular array of cylinder bores in this drum slidably receive respective pistons which cooperate with a control flange or swash plate inclined to the axis of rotation of the drum so that, upon rotation of the latter, the pistons displace hydraulic fluid through apertures in the control plate or surface and the machine constitutes a hydraulic pump.

In a hydraulic motor of the axial-piston type, hydraulic fluid is forced into the cylinder bores through the control plate or surface and, by reaction of the piston against the flange or swash plate, rotation of the drum and its shaft is carried out. Since the operating efficiency of each of these hydrostatic machines is a function of the angle inclination of the control flange to the axis of rotation of the drum, such systems are of particular suitability in variable speed transmissions. Furthermore, since the hydrostatic pump and hydrostatic motor can be coupled via only two hydraulic lines or passages over short or long distances, they can be used for compact power transmission systems, remote actuation and indication and servomechanisms.

Prior to the development described in our application Ser. No. 597,944, it had been the practice in axial-piston machines of the general character described to support the cylinder drum upon a stationary (i.e. nonrotatable) axle 3,495,542 Patented Feb. 17, 1970 or central shaft rigid with the control or valve plate or some other portion of the housing. In order to hold the cylinder drum against this plate with force increasing with the hydraulic pressure tending to separate the drum from the valve plate or apertured surface over which it slides, it was proposed in connection with the system to provide a chamber between the stationary support shaft and the drum, chamber being defined between annular surfaces of the shaft and drum. Hydraulic fluid delivered at the pressure of the high pressure side of the machine to the chamber urged to the drum against its control plate or surface.

Considerable diificulties are involved in the kinematic relationship since the bearings commonly required between the shaft and the drum must be capable of permitting rotational as Well as axial movement. Furthermore, the two types of movement prevented adequate sealing of the chamber so that complex systems were necessary to supply hydraulic fluid thereto and prevent loss of the fluid.

It is, therefore, the principal object of the present invention to provide an improved axial-piston machine in which these disadvantages are avoided.

Another object of this invention is to provide an improved method of rotatably supporting the cylinder drum of an axial piston machine whereby the sliding of the drum along its control plate or surface can be improved and pressure may be supplied to retain the drum against this plate or surface.

Still another object of this invention is to advance the principles originally set forth in our application Ser. No. 597,944 which describes the basic structure of an improved system in which the arrangement described below represents still another development.

In our earlier application, we have provided an axial piston machine which was capable of attaining the aforedescribed object with a shaft or axle of the cylinder drum which is at least limitedly axially movable within and on the housing and is keyed thereto to prevent its rotation relative to the housing. In the earlier system, the housing structure, below the control or valve plate or apertured surface, forms with the shaft at least one annular compartment communicating with at least one side of the hydraulic system for applying hydraulic pressure in axial direction to a surface of the shaft effective to draw the cylinder drum against its control plate or surface.

When reference is made hereto a control plate underlying the cylinder drum, it will be understood that this plate may be an apertured disk (With kidney-shaped ports) which is held against the housing.

Instead of a separate valve plate, however, a stationary annular zone of the housing may be constituted as a valve or control surface whose apertures receive fluid from the inlet and outlet of the housing, to distribute it to or collect it from the cylinder bores of the drum.

The machine was provided, as an important feature of the invention, with antifriction means in the thrust direction of the shaft between the latter and the cylinder drum for exerting the aforementioned axial force upon the latter. The antifriction means can include roller or ball-type thrust bearings or lubricant film bearings of a hydrostatic nature.

The bearing means journaling the cylinder drum upon the shaft need not admit of relative axial motion of the shaft andthe cylinder drum or may permit a restricted small degree of such relative motion since the shaft retains the cylinder drum against the control surface of plate and the housing. Still another feature resides in the provision of spring means between the shaft and a spring seat to bias the cylinder drum against its control plate or surface even when the hydraulic pressure delivered to the chamber falls off. This bias is important also when the device is used as a pump to ensure firm contact between the drum and the control surface on starting (when no hydraulic pressure is available). Moreover, the chamber is advantageously constructed with a pair of annular compartments in which respective shoulders of the shaft are exposed, the hydraulic pressure within these compartments acting upon the shoulders in the same direction, i.e. to draw the shaft and the cylinder drum against the control plate or surface. Each of the compartments is, moreover, provided with a respective passage communicating between the compartments and the inlet and outlet sides of the hydraulic system, respectively. Thus, at least one of these shoulders always receives the maximum pressure of the inlet or outlet (depending upon whether the device is operating as a motor or pump), While the other receives the minimum pressure of the other port. Should the inlet pressure be increased and the outlet pressure be decreased or should the inlet pressure drop while the outlet pressure increases, substantially the same force must be maintained upon the axially shifta'ble shaft.

According to the present invention, the shaft is provided with a single annular surface transverse to the axis of rotation of the drum and formed by a disk attached to the shaft or machined as a single shoulder in the latter, while both of the annular compartments, which are co axial and generally lying in the same plane perpendicular to the axis of the drum, apply the respective fluid pressures to concentric radially spaced annular zones of this bearing surface.

In a more specific feature of this invention, the annular bearing surface of the'shaft is formed at an end of the shaft remote from the thrust bearing which co-operates with the cylinder drum, i.e. at the base of the housing, which can be formed with a pair of axially extending coaxial cylindrical compartments each communicating with one of the hydraulic sides of the pump or motor. The compartments open axially in the direction of the bearing surface of the shaft which may be formed as a disk retained in place by a nut threaded onto the shaft. A spring means, e.g. one or more Belleville washers or dished-disk springs, may bear also against this surface to draw the shaft axially against the drum and to draw the latter against its control surface as previously mentioned.

A particularly effective realization of this invention provides the annular compartments in the control plate whose control surface on one side lies in sliding contact with the drum and whose opposite surface is exposed at a space in the housing accommodating the bearing surface of the shaft. In this system, the concentric compartments are formed as coaxial grooves machined in the control plate, the inner groove being somewhat deeper than the outward groove to allow a passage to be formed from the inner groove to one of the ports beneath the outer groove.

According to another feature of this invention, the sealing of the compartments can be greatly simplified by providing directly within the coaxial compartments annular flange-type seals which, in turn, bear against respective piston rings acting against the bearing surface of the shaft.

The above and other objects, features and advantages of the present invention will become more readily apparent. from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view of a hydraulic machine embodying the present invention; and

FIG. 2 is a fragmentary axial cross-sectional view of another embodiment of the system.

In FIG. 1, we show a hydrostatic machine (pump or motor) for use in a hydraulic transmission of the type described in the aforementioned patents and constructed generally as set forth in our prior application mentioned above. It should be noted that the same device may serve both as a pump and motor and a discussion of one will not exclude the other from consideration. The hydrostatic motor comprises a driven shaft 50 whose control flange 8 has an axis A intersecting the axis A of the cylinder drum at an obtuse angle oz. The housing 1 of this hydraulic machine can be mounted upon a base plate or otherwise provided with support means (not shown) for fixedly or adjustably positioning it in relation to the driven system and in relation to a hydrostatic pump whose swash plate or control flange (analogous to flange 8) is angularly adjustable. In a kinematic reversal of the system, shaft 50 may be the driving shaft of a hydrostatic pump whose associated hydrostatic motor may have a swingable swash plate or control flange. The hydraulic machine, in either case, is provided with a central chamber 1' in the housing 1 within which a control or valve plate 2 is mounted. The plate 2 is held by the cylinder drum 5 against the housing and forms at 2' an apertured surface. Passing centrally through the housing and the valve plate 2 is the shaft 11.

The valve plate 2 is provided with kidney-shaped distribution apertures 3 of the type described in the aforementioned patents and commonly known in the art. The apertures 3 communicate with passages 4' extending axially in the cylinder drum 5 to the respective cylinder bores 4. A plurality of such bores is formed integrally in the drum in angularly equispaced relationship about the shaft 11 and its axis A, such that the cylinder bores 4 are parallel to the axis A about which the drum 5 rotates. The bores 4 thus form an annular array of cylinders within which respective pistons 6 are axially slidable. The pistons 6 are joined flexibly to the control flange 8 via connecting rods 7. To this end, the rods 7 are formed with generally spheroidal heads 7' received in correspondingly shaped sockets 8' of the flange for movement relatively thereto with at least two degrees of freedom. The sockets 8 are flared outwardly at A" to clear the connecting rods 7 and prevent application of bending stresses to them.

The apertures 3 of the control plate 2 register with the axial passages 9 formed in the housing 1 axially beyond the cylinder drum 5. These passages 9 connect the apertures 3 with a pair of ports 10 which may be used interchangeably as the hydraulic inlet or hydraulic outlet of the machine depending upon the type of use to which it is put. Thus, when the system is operated as a pump and the drum 5 is driven by the shaft 50, the left-hand port 10 (FIG. 1) can be considered the outlet and the high-pressure side of the machine, whereas the other port is constituted as the inlet.

The central shaft or axle 11 is axially movable within the housing 1 (arrow 11) but is keyed to the housing, e.g. by splines 11" which prevent rotation of this shaft within the housing. An abutment flange 12 at the upper end of the housing 1 is formed on the axle shaft 11 and engages the end face 1" of the housing remote from the flange 8 to limit movement of the shaft 11 in the direction opposite that represented by the arrow 11'.

At the free end of shaft 11, proximal to the flange 8, we provide a threaded portion 13 onto which a nut 14 is secured to retain a thrust-bearing ring 15, constituting one race of the thrust-bearing B, upon the shaft 11. The other race-forming ring 16 rests axially against a shoulder 17 of the cylinder drum 5 within an axially open recess 512 at the free end of the shaft 11. The thrust-bearing B, formed by the races 15 and 16 and the roller elements 15 (e.g. bores) is thus housed in the recess 5b. A further recess 5:: extends axially inwardly from the recess 5b and forms an annular seat 18 for the dished washer or Belleville spring 19 which urges the ring 16 and the bearing B, together with the shaft 11, axially downwardly while reacting against the cylinder drum 5 to yieldably retain it against the control plate 2 and the floor 1b of the chamber 1 of housing 1. The means for rotatably mounting the cylinder drum 5 upon the axle 11 is here constituted by a pair of axially spaced needle bearings 20 respectively disposed close to the ends of the drum 5.

The central shaft 11 is provided, at its extremity remote from its free end, with a single annular shoulder 23 serving as a bearing surface of the shaft and lying in a plane perpendicular to the axis A of the shaft 11. In accordance with the present invention, the hydraulic pressure is applied to the single annular surface 23 via a pair of coaxial generally cylindrical pressure compartments 24 and 27 respectively connected via passages 25 and 28 with the ducts 9 of the ports 10. The compartments 24 and 27 are constituted as generally cylindrical grooves open in the direction of the surface 23 and receiving ringlike pistons 56 and 56' lying in a common transverse plane P and bearing directly against respective annular zones of the surface 23 in, of course, the same direction. The grooves 24 and 27 are sealed by annular flange-type seals 57 and 57. The innermost groove 27 extends axially beyond the outermost groove 24 to permit the passage 25 to run under the latter as previously noted. To further limit leakage of the hydraulic medium from chamber 27, an O-ring 29a hugs the shank portion 21 of shaft 11 respectively.

Since the pressure in the lines 9 is applied to the surface 23 in two annular zones effective in the same direction, the total pressure at the ports determines the axial force applied in the direction of arrow 11 to the shaft 11, especially when the cross-sections of the grooves 24 and 27 and the annular pressure zones have the same effective surface areas. The system operates as described in application Ser. No. 597,944.

In another embodiment of this invention, however, the cylinder drum 105 rests against a nonrotatable control plate 102 whose apertures 103 communicate with the inlet and outlet ports via passages 109 as previously described. A thrust bearing B is here provided between the head 114 of the shaft 111 and a seat 117 of the drum 105 whose pistons have been omitted but may be identical to those illustrated in and described with reference to FIG. 1. The thrust bearing comprises a ring 115 nonrotatably retained by the shaft 111, a plurality of bearing rollers 115, and a rotatable ring 116 seated against the surface 117. A needle bearing 120 journals the drum 105, whose cylinder boss 104 receives the pistons, in the manner previously described. In this embodiment, the nonrotatable control plate 102 is provided on its side remote from the drum 105, with a pair of coaxial grooves 124 and 127 extending axially parallel to the shaft 111 and opening in the direction of the bearing surface 123 of a disk 122 locked to the remote end of the shaft 111, by a nut 149. A pin 149' prevents loosening of the nut and forms an abutment for the plate 122. In this embodiment, the spring force urging the shaft 111 in the direction of arrow 111' is a Belleville washer or dished-disk spring 119 interposed between the disk 122 and the control plate 102.

A hydraulic pressure is applied to the bearing disk 122 by a pair of annular pistons 156 and 156' whose contact areas with the disk 122 are equal. The seals 157 and 157 prevent escape of fluid from the groove 124 and 127 as previously indicated. In this arrangement, however, the passages 125 and 129, connecting the groove 124 and 127 with the passages 109, are also formed in the control plate 102 and extend to the apertures 103 thereof.

The improvement described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the invention.

We claim:

1. In an axial-piston machine having a housing, a cylinder drum rotatable in said housing and provided with an annular array of angularly spaced cylinder bores surrounding the axis of rotation of the drum, said drum resting axially against a control surface, respective pistons slidably received in said bores, a nonrotatable central shaft extending through said cylinder drum and rotatably journaling same in said housing, said housing being formed with passage means with a high-pressure side and a low-pressure side communicating with said cylinder bores through said control surface, and means for applying hydraulic pressure of said high-pressure and low-pressure sides to said shaft in a direction tending to urge the cylinder drum against said control surface, the improvement which comprises:

an annular bearing surface formed on said shaft and lying in a plane perpendicular to the axis of rotation of said drum;

a pair of annular coaxial compartments formed in said housing means and open in the direction of said bearing surface while lying essentially in a common plane perpendicular to said axis of rotation and respectively communicating with said highand lowpressure sides; and

pressure-transmitting means for including a respective piston ring received in each of said compartments and acting against said bearing surface for applying the hydraulic pressure of each of said compartments to respective concentric zones of said bearing surface.

2. The improvement defined in claim 1, further comprising a respective annular seal in each of said compartments acting upon the respective piston ring and preventing escape of fluid from the respective compartment past the respective ring.

3. The improvement defined in claim 1 wherein said compartments are concentric axially extending circular grooves formed in said housing and opening in the direction of said bearing surface.

4. The improvement defined in claim 3 wherein said housing is formed with a control plate defining said control surface at one side of said plate, said grooves being formed in the other side of said plate.

5. The improvement defined in claim 3 wherein said grooves include an outer groove, and an inner groove of an axial extent greater than that of said outer groove, said housing being formed with respective channels connecting each of said grooves with a corresponding one of said sides, the channel of said inner groove passing beneath said outer groove.

6. The improvement defined in claim 1 wherein said shaft has a threaded extremity carrying said bearing surface, further comprising a disk mounted on said threaded extremity and defining said bearing surface, and a nut retaining said disk on the threaded extremity of said shaft.

7. The improvement defined in claim 6, further comprising spring means between said housing and said shaft for urging said shaft yieldably in said direction.

8. The improvement defined in claim 7 wherein said spring means includes a dished-disk spring interposed between said disk and said housing.

9. The improvement defined in claim 1 wherein said housing is formed with a control plate defining said surface, said drum resting against one side of said control plate, said compartments being formed as concentric grooves in the other side of control pl-ate open axially in said direction, said control plate being formed with respective channels connecting said grooves with the high-pressure and low-pressure sides, said shaft being provided beyond said control plate with a threaded extremity, a bearing disk mounted on said extremity and confronting said other side of said control plate, a dished-disk spring surroundng said shaft and interposed between said disk and said other side of said control plate for urging said shaft in said direction, and a nut on said threaded extremity retaining said disk thereon, said pressure-transmitting means including a respective piston ring slidably received in each of said grooves and resting 7 8 against said disk along said concentric zones, and respec- References Cited tive annular flange-type seals in each of said grooves UNITED STATES PATENTS seahng same against escape of fluid and hydrauhcally bearing against said rings, said rings being generally co- 2,738,996 3/1956 Andersson 277 73 planar, said machine further comprising thrust-bearing 5 3,253,551 5/ 1966* Thoma 103162 means interposed between the other extremity of said 3,410,220 11/1968 Kratzenberg Shaft and Said dfum- WILLIAM L. FREEH, Primary Examiner 

